Today, the solar system is pretty easy to keep track of (except for that piddling dwarf planet debate). Everything orbiting the sun has its defining features: There’s Tiny Burny One, Bigger Burny One, Home, the Red Planet, the Big One, the Ringed One, the Butt Joke, and Ol’ Blue. But as the planets change, kids are going to have a harder time keeping track of them. Especially if humans miraculously survive another 40 million years. Those middle-schoolers may have to make sense of a Mars with a ring.
Astronomers have long known that Phobos, one of Mars’ two moons, is spiraling toward the planet—about seven feet closer every 100 years. At some point, the moon will self-destruct, either crashing into the surface or disintegrating under tidal stresses from the planet’s gravitational pull. And according to an analysis published today in Nature Geoscience, those pieces—either ejecta from a plunge into the surface or the rubble from the tidal crumbling—may end up forming a new ring system around Mars. In 20 or 40 million years, that is.
Planetary rings aren’t uncommon: Although Saturn’s are the most prominent, the other three gas giants in the outer solar system have them, too. But Benjamin Black and Tushar Mittal, planetary scientists at UC Berkeley, think that Mars’ ring-to-be could rival Saturn’s in density. That’s because its source material from Phobos is so loosely packed. Astronomers are increasingly convinced that the moon is basically a pile of rocks held together by a thin crust—a crust with stretch mark-like grooves that NASA scientists think are formed by those strong tidal forces.
Once the moon breaks apart, the bigger pieces of rubble will crash into Mars, forming new craters; the rest will go to make ring. Seems like it could be beautiful; too bad nothing that looks remotely human will be around to see it. After all, 20 million years ago the closest thing to people on Earth were ape-like quadrupeds.